Among semiconductor elements, power modules used for supplying electric power exhibit comparatively high levels of heat generation, and the substrate on which these power modules are installed is typically a power module substrate having an insulating substrate formed from AlN (aluminum nitride), Al2O3 (alumina) or Si3N4 (silicon nitride) or the like, a circuit layer formed by bonding a first metal sheet to one surface of the insulating substrate, and a metal layer formed by bonding a second metal sheet to the other surface of the insulating substrate.
In this type of power module substrate, a power element semiconductor element is installed on the top of the circuit layer via a solder material.
Further, a heat sink for cooling the power module substrate is bonded to the other surface of the metal layer.
For example, Patent Document 1 proposes a power module substrate in which the first metal sheet and the second metal sheet which constitute the circuit layer and the metal layer respectively are copper sheets, and these copper sheets are bonded directly to the insulating substrate using a DBC method. Further, as illustrated in FIG. 1 of Patent Document 1, by bonding an aluminum heat sink to this power module substrate using an organic heat-resistant adhesive, a power module substrate with a heat sink is obtained.
Further, Patent Document 2 proposes a power module substrate in which aluminum sheets are used as the first metal sheet and the second metal sheet which constitute the circuit layer and the metal layer respectively. By bonding a heat sink to the metal layer of this power module substrate by brazing, a power module substrate with a heat sink can be formed.
Furthermore, Patent Document 3 proposes a power module substrate in which a metal sheet is bonded to one surface of an insulating substrate to form a circuit layer, and a casting method is used to form an aluminum heat sink directly on the other surface of the insulating substrate. Patent Document 3 also discloses the use of an aluminum sheet or a copper sheet as the metal sheet for forming the circuit layer.